1. Field of the Invention
This invention relates to herbicides. More particularly, this invention relates to biorational herbicides.
2. Background of the Invention
Controlling weeds is an agricultural management issue as ancient as food crops themselves. A weed can be defined as a plant without virtue, that is, a plant growing where it is not desired. Until science brought forth modern chemical solutions, most weed control was accomplished through brute force. Today, a wide range of chemical products have been developed in an effort to control these noxious plants. Weeds are now classified as pests and the chemical term used to describe a composition that controls weeds is "herbicide".
Weeds are of enormous economic importance. As the agricultural community deals with problematic issues, such as loss of invaluable top soil and reduction of dedicated agricultural land to ever expanding suburban housing and commercial development, the economic losses to weed infestation take on ever increasing importance.
Nearly all of modern business is affected some way by matters of weed control. Through out the world, less developed and more advanced countries alike, weed infestation results in lower crop yield and can ultimately be linked to a lower standard nutritional well being, which, in turn, can translate to ill health. If food is, in a sense, considered medicine, then the loss or reduction in yield of important food crops can initiate or prolong disease in human and animal populations.
Other lesser, yet still important impacts of weed infestation include: aesthetic diminution of public recreational and home landscape areas; increased costs associated with controlling insect, arachnid, and fungal plant diseases that accompany these annoying plants; degraded and lower quality produce; increased water allocation; additional field management problems; and reduced human and machine field efficiency.
The cost of weed infestation to mankind is much higher than is generally recognized. The presence of weeds is rather ubiquitous on all of the 500+million acres of US crop land and one billion plus acres of range land. It is estimated that weeds are responsible for agricultural losses and control costs in the United States of approximately $4 billion and $7.5 billion, respectively. Worldwide impacts are more difficult to obtain, but can safely be considered of comparable magnitude. In Canada, for example, the estimated annual loss is approximately $1 billion. These estimated losses do not include the damage caused by weeds to pastures, hay crops, and range lands, or to livestock as a result of weed related phytotoxins that affect animals.
Many herbicides presently available for use may be found in the Sixth Edition of the "Herbicide Handbook of the Weed Science Society of America", published by the Weed Society of America, 309 West Clark Street, Champaign, Ill. 61820. In general, these are synthetic chemicals that do not occur in nature. Many of these non-natural herbicides have a low LD.sub.50 value and thus are toxic to animals, particularly man. Examples of these include arsenicals (e.g., disodium methane arsenate and methylarsonic acid), substituted ureas, 2, 4-D (2, 4-dichlorophenoxy acetic acid), 2, 4-D amine, glyphosphate (N-(phosponomethyl) glycine (sold under the name ROUNDUP.RTM., Monsanto) or its isopropylamine salt. Reports suggest that ROUNDUP.RTM. herbicide is the third most common source of pesticide-related illnesses for farm workers. The product is toxic to fish and thus is not approved for use on aquatic vegetation.
Thus, it seems clear that it is generally preferred that herbicides have minimal adverse impact on the environment, other than on the target species. It would also be preferable to provide a herbicide that is a compound that exists in nature. Under recent Environmental Protection Agency guidelines, when such naturally-occurring compounds are used as herbicides, they are termed biorational herbicides. Such compounds can then be synthesized by standard organic synthetic methods.
It is clear in light of the above disclosure, that there would exist considerable economic advantage for the development of effective biorational herbicides that could be added to the current arsenal of integrated pest management (IPM) herbicides.